Thousands of passengers topping up travel cards on Glasgow's subway system have been double-charged following a "technical issue" with the payment system, it has emerged.

Customers travelling on the underground system in the city on September 17 may have been subject to a glitch in the system that took twice the amount of money from debit and credit cards.

Travellers are not being proactively informed of the problem but will be refunded, a spokesperson for SPT said.

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However, passengers have reacted with irritation to the situation and how it has been handled by the travel company.

One passenger, who asked not to be named, discovered twice the amount of expected money had been billed on her credit card.

She said: "I was shocked to discover the double payment on my credit card statement, especially as I hadn't received any communication from SPT that anything had gone wrong.

"It is ridiculous that they have not publicly owned up to this mistake.

"Although it only affected some smart card holders they could have sent am email to all customers advising them of the problem on this day.

"How many people actually check their card statements?

"People will already have had to pay their bills for the month so a refund weeks later is really not acceptable."

Nearly 4000 transactions were double-charged when people tried to top up their Subway travel cards on September 17.

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SPT said this was a "one-off" error by its third party contractor that it was not able to directly intervene in and apologised to affected customers.

An SPT spokesperson said: "We are aware of a technical issue with our card payment provider which saw 3996 transactions double charged to customer debit and credit cards on September 17, 2023. "This was a one-off error on the part of a third-party contractor responsible for administering card payments. "Our suppliers are working to process refunds for all affected customers.

"SPT does not have this within our control as we do not hold full payment card details for any customers, in line with payment security best practice."

The passenger who spoke to The Herald said she had had to proactively contact SPT for answers about the additional payment and was frustrated with the slow response and lack of an offer of compensation.

The SPT spokesperson added: "We acknowledge the refund process is taking longer than expected and we apologise to all customers affected.

"We have expressed our annoyance and disappointment that this has not been resolved more quickly by our suppliers and we continue to apply pressure to get this sorted. "It is our understanding that all refunds are currently being processed and are underway.

"All customers should receive a refund automatically without having to contact SPT."

Smart ticketing was introduced on Glasgow's Subway in autumn 2013, replacing paper magnetic strip tickets with plastic smartcards.

The joint initiative between SPT and Nevis Technologies allowed passengers to add credit to their cards at machines and tickets stations with discounted prices for using the so-called Smartcards.

At last count around 200,000 Smartcards had been issued.

One of the main gripes about the city's transport system is a lack of integrated ticketing that allows passengers to travel between bus, train and subway.

SPT has pledged that integrated ticketing is on its way and eventually Smartcards will be useable on these transport modes plus ferry - and to "buy other everyday items such as coffee and cake on your way to work."

There is, however, no date set for when this might become available.